Low-loss closed-loop supply system for transferring liquified gas from a large container to a small container

ABSTRACT

A liquified gas is transferred from a supply tank to a saddle tank by gravity flow. After a predetermined amount of the liquified gas has been transferred, gravity flow is stopped and pressure is equalized between the saddle tank and the container to be filled. Thereafter, vapor from the container flows into the supply tank causing liquified gas to flow from the saddle tank into the container. After the container has received a predetermined amount of liquified gas, liquid flow ends and pressure is equalized between the supply and saddle tanks.

I Umted States Patent [1 1 [m 3,710,584 Leonard 1 Jan. 16, 1973 54LOW-LOSS CLOSED-LOOP SUPPLY 2,487,863 11/1949 Garretson ..62/55 SYSTEMFOR TRANSFERRING 3,034,308 /1962 Littlewood ..62/54 3,369,371 2/1968Holly et al. ..62/54 ARGE 2,632,302 3/1953 Steele ..62/55 CONTAINERPrimary ExaminerMeyer Perlin [75] Inventor: Kenneth R. Leonard, Boulder,Colo. Assistant ExaminerRonald C. Capossela [73] Assignee: CryogenicEngineering Company, Atwmey 6nffin Bramgan & Kmdness Denver, Colo. 57]ABSTRACT [22] Flled: 1970 A liquified gas is transferred from a supplytank to a [21] App]. No.: 83,460 saddle tank by gravity flow. After apredetermined amount of the liquified gas has been transferred, gravityflow is stopped and pressure is equalized between 62/ gig 73; the saddletank and the container to be filled. Thereafter, vapor from thecontainer flows into the [58] Field of Search "220/85 igl f g gg gisupply tank causing liquified gas to flow from the saddle tank into thecontainer. After the container has received a predetermined amount ofliquified gas, [56] References Clted liquid flow ends and pressure isequalized between the UNITED STATES PATENTS pp and saddle tanks-3,l06,07l /1963 Green et al ..62/55 Claims, 6 Drawing Figures ll 18 i 376| 2 -VENT 4| SUPPLY TANK 39 Mg 5' UOUID IN 23 3 49 1' I I7 k 4 I 15 I9I F L 53 6, 45 43 SADDLE TANK l3 2 Q- 7 s7 '16 PRESSURE REGULATING VAWEPATENTEDJMI 16 I915 SHEET 1 OF 3 FIG] UQJID IN SUPPLY TANK W -wi FIG. 2

INVENTOR KENNETH R. LEONARD Q fi BY ATTORNEYS PATENTEHJAN 16 I9733.710.584

sum 2 or 3 VAPOR FIG. 4

VAPOR PSIG PSI INVENTOR KENNTH R. LEONARD ATTORNEYS FATENTEDJMI I 6 I973SHEET 3 0F 3 SUPPLY TANK E TANK PRESSURE REGULAIING VALVE LOW-LOSSCLOSED-LOOP SUPPLY SYSTEM FOR TRANSFERRING LIQUIFIEI) GAS FROM A LARGECONTAINER TO A SMALL CONTAINER BACKGROUND OF THE INVENTION Thisinvention relates to a method and apparatus for filling small containersfrom large containers and more particularly to a method and apparatusfor filling a small container with liquified gas from a large container,without the loss of gas vapor.

It is often necessary to transfer liquified gases from larger containersto smaller containers. For example, oxygen converters used forconverting liquified oxygen (LOX) to a gas for use by the crews of highaltitude aircraft are usually filled from larger tanks; and, in thisregard, objects of this invention are to provide a new and improvedmethod and apparatus for transferring a liquified gas from one containerto another.

Many of the transferred gases are quite volatile and tend to boil offrapidly during conventional transfer methods. Hence, because many ofthese gases are also quite expensive to produce, it is another object ofthis invention to provide a particularly low-loss method of transferringa liquified gas from a large container to a small container.

Some liquified gas vapors that are released during conventional transfermethods are highly dangerous because they readily support combustion. Inaddition, flammable gases such as hydrogen and natural gas often must betransferred from large containers to small containers for use atparticular locations. If gas vapors are released during the transfer offlammable gases, they produce a highly dangerous environment because ofboth combustability and possibly inhalation. Consequently, it is anotherobject of the invention to provide a safer method and apparatus forperforming the desired transfer without vapor of the transferred gasboiling off into the atmosphere.

It is still a further object of this invention to provide a new methodand apparatus for transferring cryogenic fluids in a manner which doesnot require expensive cryogenic pumps so as to further reduce boil offlosses.

SUMMARY OF THE INVENTION In accordance with principles of thisinvention, the liquified gasis first transferred from a supply tank toan intermediate tank by gravity flow. After a predetermined amount ofthe liquified gas has been transferred in this manner, pressure isequalized between the intermediate tank and the container to be filled.Thereafter, pressure from the container is bled down into the supplytank causing liquified gas to flow from the intermediate tank into thecontainer. Transfer is ended after the container has received a desiredamount of liquified gas. Thereafter, pressure is equalized between thesupply and intermediate tanks, and the cycle is repeated to fill asecond container.

In accordance with other principles of this invention, the supplycontainer and the intermediate container are vacuum insulated, as arethe lines interconnecting the supply tank, the intermediate tank and theconverter so as to further conserve gas by preventing boiloff loss.

It will be appreciated from the foregoing summary that the inventionprovides an uncomplicated method liquid gas from a supply container ortank to a smaller container or converter with low vapor loss. Byutilizing the pressures in the tanks and gravity to cause the liquifiedgas to flow, the need for an expensive cryogenic pump is eliminated. Inaddition, the high boil-off associated with the use of cryogenic pumpsis also eliminated.

While the illustrated use of the herein described invention is totransfer LOX from a supply container to a converter, and thus reduce thevapor danger associated with such transfers, it will be appreciated thatthe invention can be utilized to transfer other types of liquifiedgases. For example, the invention can be utilized to transfer flamableliquified gases, such as hydrogen and natural gas.

BRIEF DESCRIPTION OF THE DRAWINGS 'taken in conjunction with theaccompanying drawings,

- wherein:

and equally uncomplicated apparatus for transferring a FIG. 1 is aschematic diagram illustrating a preferred embodiment of the invention;

FIGS. 2, 3, and 4 are schematic diagrams illustrating the sequence oftransfer between the supply container and the container to be filled;

FIG. 5 is a schematic diagram of a condensing system for use with theembodiments of the invention illustrated in FIGS. 1 and 6; and,

FIG. 6 is a schematic diagram illustrating an alternate embodiment of aportion of the structure illustrated in FIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT FIG. 1 illustrates a preferredembodiment of the invention and comprises: a supply tank 11; anintermediate tank 13; a converter 15; four primary valves 17,.18, 19 and21; four secondary valves 23, 25, 27 and 29; an automatic valve 31; twopressure relief valves 33 and 35; a rupture disc 37; and, three pressureindicators designated P1, P2 and P3.

The supply tank has a liquid input/output line 39 and a vaporinput/output line 41', the intermediate tank 13 which is of thesaddle-type has a liquid input/output line 43 and a vapor input/outputline 45; and, the converter has a liquid input/output line 47 and avapor input/output line 49. The liquid input/output line 39 of thesupply tank is connected by pipes through the first secondary valve 23and a filter 51 to an input connection. The input connection allowsliquified oxygen (or another liquified gas, as the case may be) to beinserted into the supply tank 11 to fill that tank. The liquidinput/output line 39 of the supply tank 11 is also connected by pipesthrough the first primary valve 17 and a first supply saddle couplingmember 53 to the liquid input/output line 43 of the saddle tank 13. Thevapor input/output line 45 of the saddle tank 13 is connected by pipesthrough a second supply/saddle coupling member 55 and the second primaryvalve 18 to the vapor input/output line 41 of the supply tank 1 l.

A pressure sensor 57, located in the saddle tank, is connected by pipesthrough a heat exchanger coil 58, a pressure regulating valve 59, andthe second secondary valve 25 to the pipe line connecting the vaporinput/output lines of the saddle and supply tanks 11 and 13. The samepipe line is also connected to P2 and through the first pressure reliefvalve 33 to a vent output. The vapor input/output line 41 of the supplytank 11 is also connected by a pipe through the third secondary valve 27to the vent output, through the second pressure relief valve 35 to thevent output and through the rupture disc 37 to the vent output. Inaddition, the vapor input/output line 41 of the supply tank 11 isconnected to P1. The liquid input/output line 39 of the supply tank 11is connected by a pipe through the fourth secondary valve 29 and a heatexchanger coil 61 to the vapor input/output line 41 of the supply tank 11.

The liquid input/output line 43 of the saddle tank 13 is connected bypipes through a saddle-converter coupling member 63 to a first terminalon one side of the automatic valve 31. The liquid input/output line ofthe supply tank 39 is connected by pipes through the third primary valve19 and a supply/converter coupling element 65 to a second terminal onthe same side of the automatic valve 31. The fourth primary valve 21 isin a pipe connected across the first and second terminals on this sameside of the automatic valve 31. In addition, P3 is connected to the pipeline that connects the liquid input/output line 39 of the supply tank 11to the automatic valve 31. The other side of the automatic valve 31 isconnected by pipes to the liquid and vapor input/output lines 47 and 49of the converter 15.

All of the pipe lines connecting the supply tank to the saddle tank andconnecting the supply and saddle tanks to the converter are vacuuminsulated to prevent undesirable boil-off. The remaining lines are notillustrated as being insulated, however, they may be insulated, ifdesired. The insulated lines connecting the supply tank and the saddletank and the converter form the primary apparatus of the invention andare utilized to carry out the method as hereinafter described withrespect to FIGS. 2, 3, and 4. The remaining lines provide a means forfilling the supply tank as well as for venting the various vapor linesand tanks as necessary to the normal operation of a liquified gassystem, as will be understood by those skilled in the art. For example,the first pressure relief valve 33 provides pressure relief for thesaddle tank. Similarly, the second pressure relief valve 35 providespressure relief for the supply tank. The heat exchanger coil 58 and 61allows vaporization of the liquid to build pressure in their respectivesaddle and supply tanks, when desired.

Turning now to a description of the operation of the apparatusillustrated in FIG. 1 for carrying out the method of the invention; itis initially assumed that the pressure in both the supply tank and thesaddle tank is zero psig. In addition, it is assumed that the pressurein the converter tank is in the range of 50-100 psig. Similarly, it isassumed that the temperature of the converter is substantially atliquified oxygen temperature. Moreover, in accordance with theprinciples of the invention, the saddle tank is at a lower elevationthan the supply tank.

The first step of the method of the invention is the opening of thefirst and second primary valves 17 and 18 (FIG. 2). When this occurs,the liquid flows by gravity from the supply tank 11 through the firstvalve 17 into the saddle tank and vapor flows from the saddle tankthrough the second valve 18 into the supply tank.

When the desired amount of liquid has flowed from the supply tank to thesaddle tank, the first and second primary valves 17 and 18 are closed.This liquid-vapor flow increases pressure slightly in both tanks toabout 3-5 psig, for example.

Next the converter 15 is coupled to the system and the automatic valve31 and the fourth primary valve 21 are opened. In accordance with thisstep of the method (FIG. 3), pressure is equalized between the converterand the saddle tank through the saddle/converter coupling element 63.When the pressure in these two tanks has equalized, they will both be ata value of, for example, 30 psig, depending upon the size of the tanks.

In accordance with the method of the invention, after equalizationbetween the converter and the saddle tank has been completed, the fourthprimary valve 21 is closed and the third primary valve 19 is opened(FIG. 4). When the third primary valve is opened and the fourth primaryvalve is closed, the pressure differential between the converter 15 andthe supply tank 11 causes vapor to flow from the converter 15 to thesupply tank 11. This action causes liquid to flow from the saddle tank13 into the converter 15. Any vapor produced by this liquid flow passesinto the supply tank 11 and bubbles through the liquid phase in thesupply tank to cause turbulence in the supply tank which reduces thermalStratification and undue pressure rise in the supply tank. To preventreverse vapor flow from the converter 15 to the saddle tank 13 a one-wayvalve 67 is included in the automatic valve 31.

When the converter has filled to a satisfactory level, the third primaryvalve 19 is closed. In addition, the automatic valve 31 is closed andthe converter is disconnected. The second primary valve 18 is thenopened to bring the pressure in the saddle tank down to the pressure inthe supply tank. Because of the accumulation of vapor in these insulatedtanks, the pressure in the tanks will rise, up to 20 psig, for example.

When it is desired to fill another converter from the supply tank, theforegoing cycle is repeated. However, in this case, the supply tankstarts at an initial pressure of about 20 psig. Hence, at the end of thefilling of the second converter, the pressure in the supply and saddletanks will be about 40 psig, for this example. Consequently, ultimately,it will become necessary to reduce the pressure in the supply and saddletanks.

Pressure in the supply tank 11 and intermediate tank 13 is, preferably,reduced by either of two methods. In accordance with the first method,these tanks are removed to a remote area and bled down by allowing theoxygen vapor to be vented into the atmosphere. In accordance with thesecond method, the tanks may be provided with condensing loops 70 and 71in FIG. 5 for circulating liquified nitrogen from a nitrogen supply tank72.

In the above regard, liquified nitrogen from the condensing fluid tank72 is directed bymeans of suitable valving, not shown, through insulatedlines 74 and 75 into the loops 70 and 71 where the tank vapors arecondensed in the tanks themselves. The nitrogen vapors are then ventedto the atmosphere as illustrated in the FIG. 5 schematic. In this mannerthe pressures in the supply and saddle tanks are not only reduced tosubstantially zero but the tank vapors are condensed and recoveredwithout the possible danger of their being released into the atmosphere.

When the method of the invention is used with the abovedescribedstructure vapor from the converter flows out of end 78 of line 43 afterthe converter is coupled to the system and valves 21 and 31 are opened.Hence, the vapor from 78 flows upwardly through the saddle tanks liquidto cause turbulence which, in many cases, is undesirable. Note in thisregard, that the intermediate tank 13 is not a long term storage tankand, therefore, does not have the thermal Stratification problems of thesupply tank 11. Consequently, although it can be advantageous for vaporto bubble through the liquid phase of the supply tank, this is notgenerally the case with the intermediate tank.

The FIG. 6 structure eliminates both the bubbling of vapor from theconverter 15 through the saddle tanks liquid phase and eliminates theneed for the FIG. 1 embodiments valve 21. In this regard, the FIG. 6embodiment includes a vacuum insulated line 80 extending between point82 on the supply tank s line 39 and point 84 at the top of thesaddle-type intermediate tank 13. The line 80 includes a one-way checkvalve 86 for permitting vapor to flow only in the direction of the arrow(toward point 84); and does not include either a valve such as 21 or aline extending between the converters liquid-input and vapor-outputlines. The remainder of the FIG. 6 embodiment is the same as FIG. 1 andwill not be further described.

The operation of the FIG. 6 embodiment is similar to that of FIG. 1. Inthis regard, liquid is first transferred from the supply tank to theintermediate tank and the pressure therebetween is equalized before thesupply and saddle tanks are isolated. Next, the converter is coupled tothe system at coupling elements 63 and 65; and vapor from converter 15flows into the top of the saddle tank 13 through line 80 and the checkvalve 86. When the pressure in these tanks is thusly equalized, valve 19is opened to permit vapor from converter 15 to flow into the supply tank11 in the same manner as was described in connection with the firstembodiment. Similarly, as the pressure in the converter drops, fluidfrom the saddle tank is forced through line 43 and check valve 67 intothe converter. It should be noted that the check valve 86 prevents thevapor from the saddle tank from flowing at this time into either thesupply tank or the converter. In other respects, operation of the twoembodiments is the same.

It will be appreciated from the foregoing description that the inventioncomprises a method and apparatus for filling a small container orconverter from a large container or supply tank. In general, the methodcomprises the steps of: equalizing the pressure between first and secondvessels in the supply system; transferring liquid from the first vesselto the second vessel and transferring vapor from the second vessel tothe first vessel; isolating the first vessel from the second vessel;equalizing the pressure between the second vessel and the container forreceiving the liquified gas; isolating the vapor phase of the secondvessel from the vapor phase of the container for liquified gas;connecting the first vessel to the container; connecting the secondvessel to the container for liquified gas so that liquid from saidsecond vessel flows into said container while vapor from the containerflows into the first vessel; and, isolating the container from saidfirst and second vessels. It will be appreciated that this method hascertain advantages in that it eliminatesthe necessity for pumping theliquified gas from one vessel to a second vessel. In addition iteliminates some of the other inherent disadvantages of former suchsystems. Moreover, because constant interconnections are provided, vaporloss is greatly reduced over prior art container filling systems; andthe method also has the advantage of reducing Stratification in thesupply tank.

In addition to being an uncomplicated method, the invention alsoprovides for safe recovery of the supply tank vapors; and providesuncomplicated apparatus for carrying out the method in that only a smallquantity of interconnecting lines and valves are utilized to carry outthe method of the invention.

While a preferred embodiment of the invention has been illustrated anddescribed, it will be appreciated by those skilled in the art and othersthat various changes can be made therein without departing from thespirit and scope of the invention.

For example, although the vapor condensation step has been described interms of both supply tank 1 1 and saddle tank 13, it will be apparentthat where the vapor phases of the two tanks are connected together asby valve 18, the condensation step can take place by connection ofeither tank into one of the loops 70.

The embodiments of the invention in which an exclu sive property orprivilege is claimed are defined as follows:

1. A low-loss method of filling a container for liquified gas from asupply system comprising the steps of:

transferring liquid from a first vessel into a second vessel, andtransferring vapor from said second vessel to said first vessel wherebythe pressure between said first and second vessels remains equalized assaid liquid is transferred;

isolating said first vessel from said second vessel;

equalizing the pressure between said second vessel and said containerfor liquid gas; connecting said first vessel to said container forliquified gas to permit vapor to flow therebetween;

connecting said second vessel to said container for liquified gas sothat said liquid from said second vessel flows into said container forliquified gas, and maintaining the connection between said first vesseland said container for liquified gas to permit vapor from said containerfor liquified gas to flow into said first vessel.

2. A low-loss method of filling a container for liquified gas from asupply system as claimed in claim 1 including the additional step of:

disconnecting said container for liquified gas from said first andsecond vessels.

3. A low-loss method of filling a container for liquified gas from asupply system as claimed in claim 1 wherein said liquified gas is liquidoxygen.

4. The method of claim 1 including the step of connecting the vaporphase of said container to the vapor phase of said second vessel duringsaid step of equalizing the pressure between said second vessel and saidcontainer.

5. The method of claim 1 including the step of isolating the vapor phaseof said second vessel from the vapor phase of said container after saidstep of equalizing the pressure between said second vessel and saidcontainer.

6. A low-loss method of filling a container for liquified gas from asupply system as claimed in claim 1 wherein said liquid is transferredfrom said first vessel into said second vessel by gravity.

7. A low-loss method of filling a container for liquified gas from asupply system as claimed in claim 6 wherein said liquified gas isliquified oxygen.

8. The method of claim 1 including the step of condensing vapors from atleast one of said first and second vessels.

9. The method of claim 8 including the step of returning the condensateto the liquid phase of at least one of said first and second vessels.

10. The method of claim 1 including an additional equalization stepafter said container is filled wherein the vapor phases of said firstand second vessels are connected to bring the pressure of said secondvessel down to the pressure of said first vessel.

11. The method of claim 10 including the step of condensing vapors fromat least one of said first and second vessels.

12. The method of claim 11 including the step of returning thecondensate to the liquid phase of at least one of said first and secondvessels.

13. A pump-free low-loss supply system for filling a container forliquified gas comprising:

a supply tank for housing said liquified gas;

an intermediate tank for temporarily storing said liquified gas;

first interconnecting means for interconnecting said intermediate tankto said supply tank for allowing liquid to flow from said supply tank tosaid intermediate tank and vapor to flow from said intermediate tank tosaid supply tank; and

second interconnecting means for interconnecting said intermediate tankand supply tank to said container so as to allow gas from said containerto flow from said container to said intermediate tank and thereafterallow liquid from said intermediate tank to flow into said containerwhile vapor from said container for liquified gas flows into said supplytank, said liquid being transferred pump-free from said supply tank tosaid container.

14. A low-loss supply system for filling a container for liquified gasas claimed in claim 13 wherein said liquified gas is liquified oxygen.

15. A low-loss supply system for filling a container for liquified gasas claimed in claim 13 wherein said intermediate tank is mounted at alower elevation than said supply tank whereby liquid flows from saidsupply tank to said intermediate tank by gravity.

16. A low-loss supply system for filling a container for liquified gasas claimed in claim 15 wherein:

said supply tank includes an input/output vapor line and an input/outputliquid line;

said intermediate tank includes an input/output vapor line and aninput/output liquid line; and,

said first interconnecting means comprises:

a first valve;

a first pipeline for interconnecting said first valve, said input/outputvapor line of said supply tank and said input/output vapor line of saidintermediate tank;

a second valve; and,

a second pipeline for interconnecting said input/output liquid line ofsaid supply tank, said second valve and said input/output liquid line ofsaid intermediate tank.

17. A low-loss supply system for filling a container for liquified gasas claimed in claim 16 wherein said second interconnecting meanscomprises:

a third valve;

a fourth valve having first and second terminals on a first side andfirst and second terminals on a second side, the first terminal on saidfirst side connected through an intermediate valve to the first terminalon said second side and the second terminal on said first side connectedthrough another intermediate valve to the second terminal on the secondside;

a third pipeline, said third pipeline interconnecting the input/outputliquid line of said supply tank, said third valve and the first terminalon the first side of said fourth valve;

a fourth pipeline, said fourth pipeline interconnecting the input/outputliquid line of said intermediate tank to the second terminal on thefirst side of said fourth valve; and,

a fifth valve, interconnecting the first and second terminals on thefirst side of said fourth valve, the first and second terminals of thesecond side of said fourth valve connected to said container.

18. A low-loss supply system for filling a container for liquified gasas claimed in claim 17 wherein said liquified gas is liquified oxygen.

19. A low-loss supply system for filling a container for liquified gasas claimed in claim 17 wherein said supply tank-and said intermediatetank are cryogenic storage vessels and wherein said first, second, thirdand fourth pipelines are insulated pipelines.

20. The structure of claim 13 including condensing loop means forcondensing vapors from at least one of said tanks.

21. The structure of claim 20 wherein said loop means is located so thatcondensed vapors are returned to the liquid phase of one of said tanks.

22. The structure of claim 20 wherein said loop means is located insideof one of said tanks.

23. The structure of claim 13 including:

a source of condensing fluid;

a condenser; and

. means for directing said condensing fluid to said condenser located sothat vapors from at least one of said tanks is brought into contacttherewith and causes said vapors to condense.

24. The structure of claim 23 wherein said condenser is located so thatcondensed vapors are returned to the liquid phase of one of said tanks.

25. The structure of claim 23 wherein said condenser is located insideof one of said tanks.

26. The structure of claim 13 wherein said second interconnecting meansincludes a pipeline for connecting the vapor phase of said container tothe vapor phase of said intermediate tank.

27. The structure of claim 26 including a one-way valve in said pipelinefor preventing the flow of gas in said pipeline in a direction out ofsaid intermediate tank.

28. The structure of claim 26 including:

a source of condensing fluid;

is located so that condensed vapors are returned to the liquid phase ofone of said tanks.

30. The structure of claim 29 wherein said condenser is located insideof one of said tanks.

1. A low-loss method of filling a container for liquified gas from asupply system comprising the steps of: transferring liquid from a firstvessel into a second vessel, and transferring vapor from said secondvessel to said first vessel whereby the pressure between said first andsecond vessels remains equalized as said liquid is transferred;isolating said first vessel from said second vessel; equalizing thepressure between said second vessel and said container for liquid gas;connecting said first vessel to said container for Liquified gas topermit vapor to flow therebetween; connecting said second vessel to saidcontainer for liquified gas so that said liquid from said second vesselflows into said container for liquified gas, and maintaining theconnection between said first vessel and said container for liquifiedgas to permit vapor from said container for liquified gas to flow intosaid first vessel.
 2. A low-loss method of filling a container forliquified gas from a supply system as claimed in claim 1 including theadditional step of: disconnecting said container for liquified gas fromsaid first and second vessels.
 3. A low-loss method of filling acontainer for liquified gas from a supply system as claimed in claim 1wherein said liquified gas is liquid oxygen.
 4. The method of claim 1including the step of connecting the vapor phase of said container tothe vapor phase of said second vessel during said step of equalizing thepressure between said second vessel and said container.
 5. The method ofclaim 1 including the step of isolating the vapor phase of said secondvessel from the vapor phase of said container after said step ofequalizing the pressure between said second vessel and said container.6. A low-loss method of filling a container for liquified gas from asupply system as claimed in claim 1 wherein said liquid is transferredfrom said first vessel into said second vessel by gravity.
 7. A low-lossmethod of filling a container for liquified gas from a supply system asclaimed in claim 6 wherein said liquified gas is liquified oxygen. 8.The method of claim 1 including the step of condensing vapors from atleast one of said first and second vessels.
 9. The method of claim 8including the step of returning the condensate to the liquid phase of atleast one of said first and second vessels.
 10. The method of claim 1including an additional equalization step after said container is filledwherein the vapor phases of said first and second vessels are connectedto bring the pressure of said second vessel down to the pressure of saidfirst vessel.
 11. The method of claim 10 including the step ofcondensing vapors from at least one of said first and second vessels.12. The method of claim 11 including the step of returning thecondensate to the liquid phase of at least one of said first and secondvessels.
 13. A pump-free low-loss supply system for filling a containerfor liquified gas comprising: a supply tank for housing said liquifiedgas; an intermediate tank for temporarily storing said liquified gas;first interconnecting means for interconnecting said intermediate tankto said supply tank for allowing liquid to flow from said supply tank tosaid intermediate tank and vapor to flow from said intermediate tank tosaid supply tank; and second interconnecting means for interconnectingsaid intermediate tank and supply tank to said container so as to allowgas from said container to flow from said container to said intermediatetank and thereafter allow liquid from said intermediate tank to flowinto said container while vapor from said container for liquified gasflows into said supply tank, said liquid being transferred pump-freefrom said supply tank to said container.
 14. A low-loss supply systemfor filling a container for liquified gas as claimed in claim 13 whereinsaid liquified gas is liquified oxygen.
 15. A low-loss supply system forfilling a container for liquified gas as claimed in claim 13 whereinsaid intermediate tank is mounted at a lower elevation than said supplytank whereby liquid flows from said supply tank to said intermediatetank by gravity.
 16. A low-loss supply system for filling a containerfor liquified gas as claimed in claim 15 wherein: said supply tankincludes an input/output vapor line and an input/output liquid line;said intermediate tank includes an input/output vapor line and aninput/output liquid line; and, said first interconnecting meanscomprises: a firSt valve; a first pipeline for interconnecting saidfirst valve, said input/output vapor line of said supply tank and saidinput/output vapor line of said intermediate tank; a second valve; and,a second pipeline for interconnecting said input/output liquid line ofsaid supply tank, said second valve and said input/output liquid line ofsaid intermediate tank.
 17. A low-loss supply system for filling acontainer for liquified gas as claimed in claim 16 wherein said secondinterconnecting means comprises: a third valve; a fourth valve havingfirst and second terminals on a first side and first and secondterminals on a second side, the first terminal on said first sideconnected through an intermediate valve to the first terminal on saidsecond side and the second terminal on said first side connected throughanother intermediate valve to the second terminal on the second side; athird pipeline, said third pipeline interconnecting the input/outputliquid line of said supply tank, said third valve and the first terminalon the first side of said fourth valve; a fourth pipeline, said fourthpipeline interconnecting the input/output liquid line of saidintermediate tank to the second terminal on the first side of saidfourth valve; and, a fifth valve, interconnecting the first and secondterminals on the first side of said fourth valve, the first and secondterminals of the second side of said fourth valve connected to saidcontainer.
 18. A low-loss supply system for filling a container forliquified gas as claimed in claim 17 wherein said liquified gas isliquified oxygen.
 19. A low-loss supply system for filling a containerfor liquified gas as claimed in claim 17 wherein said supply tank andsaid intermediate tank are cryogenic storage vessels and wherein saidfirst, second, third and fourth pipelines are insulated pipelines. 20.The structure of claim 13 including condensing loop means for condensingvapors from at least one of said tanks.
 21. The structure of claim 20wherein said loop means is located so that condensed vapors are returnedto the liquid phase of one of said tanks.
 22. The structure of claim 20wherein said loop means is located inside of one of said tanks.
 23. Thestructure of claim 13 including: a source of condensing fluid; acondenser; and means for directing said condensing fluid to saidcondenser located so that vapors from at least one of said tanks isbrought into contact therewith and causes said vapors to condense. 24.The structure of claim 23 wherein said condenser is located so thatcondensed vapors are returned to the liquid phase of one of said tanks.25. The structure of claim 23 wherein said condenser is located insideof one of said tanks.
 26. The structure of claim 13 wherein said secondinterconnecting means includes a pipeline for connecting the vapor phaseof said container to the vapor phase of said intermediate tank.
 27. Thestructure of claim 26 including a one-way valve in said pipeline forpreventing the flow of gas in said pipeline in a direction out of saidintermediate tank.
 28. The structure of claim 26 including: a source ofcondensing fluid; a condenser; and, means for directing said condensingfluid to said condenser located so that vapors from at least one of saidtanks is brought into contact therewith and causes said vapors tocondense.
 29. The structure of claim 28 wherein said condenser islocated so that condensed vapors are returned to the liquid phase of oneof said tanks.
 30. The structure of claim 29 wherein said condenser islocated inside of one of said tanks.